The New STM32L4+ Microcontroller

Alasdair Allan
2 min readNov 24, 2017

STMicroelectronics has just announced an upgrade to their STM32L4 Cortex-M4 microcontrollers with the new STM32L4+ series. The new chips operate up to 120 MHz, and have more embedded memory—up to 2 MB of flash memory and 640kB of SRAM.

The STM32L4+ series. (📷: STMicroelectronics)

Aimed squarely at the connected device market, the power consumption of the new processor is low. In ultra-low power mode with just back-up registers active it draws just 20 nA without the real‐time clock (RTC), or 200 nA with the RTC. Operating in ultra-low with 64kB of RAM the chip draws around 1μA, while in dynamic run mode it draws 43μA. Wake‐up time is around 5 μs.

Applications developed for the earlier STM32L4 microcontrollers can run unchanged on the new devices, but with improved performance. Developers used to the STM32 can use the same development tools, such as ST-Link and STM32CubeL4, that they’re used to using. However while the new processor is software compatible it is only “mostly” pin-compatible so it is not entirely a drop in replacement for the older processor.

The chips include a new Chrom-GRC (Graphics Resource Cutter) engine and a MIPI DSI controller. Optimising for non-rectagular displays the Chrom-GRC makes the new STM32+ chips a good fit for smartwatches and other wearables with small embedded displays.

Nucleo board (left), Discovery kit (middle), and the Evaluation board (right). (📷: STMicroelectronics)

The STM32L4+ has been launched alongside three evaluation boards. The Nucleo board, which comes with Arduino Uno form factor headers, a more fully-featured Discovery Kit targeted at wearable developers which has a 24 bpp round LCD (1.2 inch and 390×390 pixel), 16Mb on-board PSRAM, 512Mb Octo-SPI Flash memory interface, and finally the STM32L4+ evaluation kit which is a complete demonstration and development platform.

STMicroelectronics is already ramping up production of the STM32L4+ series, with price per unit starting at $6.52 for orders of 10,000 pieces.